The toys that you build not necessarily have to make the users happy, but it needs to connect at some emotional level. The more visceral the emotion, the better is the connection. For example, I'm never happy when I use blind in fact it mostly just makes me depressed. But it invokes a deep emotional reaction that I want to go back to using it time and again. Similarly, the echo chambers in social media don't make people happy but provide an emotional vent that makes these applications a huge success.